Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/124—Duplicating or marking methods; Sheet materials for use therein using pressure to make a masked colour visible, e.g. to make a coloured support visible, to create an opaque or transparent pattern, or to form colour by uniting colour-forming components
  • B41M5/132—Chemical colour-forming components; Additives or binders therefor
  • B41M5/155—Colour-developing components, e.g. acidic compounds; Additives or binders therefor; Layers containing such colour-developing components, additives or binders
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/62—Macromolecular organic compounds or oligomers thereof obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/66—Coatings characterised by a special visual effect, e.g. patterned, textured
  • D21H19/70—Coatings characterised by a special visual effect, e.g. patterned, textured with internal voids, e.g. bubble coatings
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/914—Transfer or decalcomania
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/27—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.]
  • Y10T428/273—Web or sheet containing structurally defined element or component, the element or component having a specified weight per unit area [e.g., gms/sq cm, lbs/sq ft, etc.] of coating
  • Y10T428/277—Cellulosic substrate

Definitions

• This invention relates to a method for coating a web of sheet material, such as paper or board, with a coating composition comprising particulate solid material suspended in a liquid carrier.
• any tendency for the coating composition to exhibit an unworkably high viscosity may be overcome at the coating head by maintaining the suspension in a state of shear, but difficulties may still arise in other parts of the system where it is not always feasible to provide the necessary shear conditions. In practice therefore, viscosity requirements impose limitations on the solids content of such suspensions, whether or not they are thixotropic in character.
• the particular solids content at which the viscosity becomes excessively high for satisfactory coating varies with the rheology of the material concerned and with the nature of the liquid carrier (which is normally water).
• a clay having a platelet structure will generally coat at a higher solids content in aqueous suspension than a pigment such as titanium dioxide where the particulate structure is irregular.
• the rheology of the clay has hitherto been found to impose an upper limit on the clay content of the coating suspension of about 45%.
• a method of coating sheet material with a coating composition comprising particulate solid material suspended in a liquid carrier, wherein the coating composition is applied to the sheet material as a foam and subsequently dried, the air content of the foam being such that the viscosity of the coating composition is greater in its unfoamed state than in the foamed stated in which the composition is applied.
• the present method may for example be used for applying art paper coating compositions, and coating compositions for producing color developer sheets for pressure sensitive copying systems, for example acidic clay or phenolic resin compositions.
• the air content of the foam which will have the effect of lowering the viscosity of the coating composition varies somewhat with the nature and solids content of the coating composition.
• the air content is preferably not more than 30%, although even in this range, the preferred air content varies widely depending on the constituents of the composition.
• foaming with a low air content initially lowers the viscosity of the composition, but increasing air content eventually causes a rise in viscosity, and an air content is reached at which the viscosity of the foamed composition is greater than that of the unfoamed composition (use of such a composition is not of course within the scope of the present invention).
• the present invention has so far been found to permit greater control and reproducibility of coating operations at high solids content than is achievable with an unfoamed coating composition. This is thought to be due to the fact that for a high viscosity composition, e.g. 3,000 cP a small unintentional change in water content of the composition (such as inevitably occurs sometimes in commercial production) results in a large change in viscosity, which can considerably affect the coatweight applied and the coating pattern achieved. At the lower viscosities achievable by the present method, however, a small change in water content has a much smaller effect on viscosity, and hence control of the coating operation is facilitated.
• a high viscosity composition e.g. 3,000 cP
• a small unintentional change in water content of the composition results in a large change in viscosity, which can considerably affect the coatweight applied and the coating pattern achieved.
• a small change in water content has a much smaller effect on viscosity, and hence control of the coating operation is
• An aqueous dispersion of 64% solid material was prepared from the following components:
• the above composition is of a kind commonly used in the production of art paper, apart from the foaming agent.
• Preparation was effected by first dissolving the dispersants in the water in a first mixing tank and then dispersing the China Clay and calcium carbonate with vigorous stirring to form a slurry. The ammonium hydroxide and binder were then added and the slurry transferred to a second mixing tank where the foaming agent was added with slow stirring to produce a foamed aqueous suspension.
• Table I shows the relationship between solids content, air content and viscosity for the suspension obtained.
• the mix was coated onto 49 g/m 2 base paper at a coat weight of about 10 g/m 2 both by conventional trailing blade and flexible blade coating methods on a pilot plant coater.
• the coater had a re-circulation loop applicator system consisting of a catch pan into which both fresh unfoamed suspension and excess suspension removed by the blade were fed.
• a mixture of the fresh and excess mix was pumped from the catch pan to the applicator system via a diffuser air addition system, a high shear disc mixer, a tube foaming unit and an air content measuring device.
• the system was closed to the atmosphere and had a minimum of "dead" flow zones, in order to maintain foam consistency as far as possible.
• Such a coater is shown in more detail in FIGS. 1 and 2 of the copending application for U.S. Patent in the name of George Douglas Robertson, Ser. No. 590,681, filed June 26, 1975 (now U.S. Pat. No. 4,038,445, issued July 26, 1977).
• the coated paper was found to be free from cockle, and had good coating pick, surface smoothness and improved coating profile.
• aqueous dispersion of 55% solids material was prepared and coated onto 49 g/m 2 base paper in the manner described in Example I, but with different components in the dispersion as follows:
• the above composition is of a kind commonly used in the production of art paper, apart from the foaming agent.
• the binder system used had the effect of increasing the viscosity of the unfoamed suspension.
• This example relates to an aqueous suspension of an acidic reactive clay suitable for use as a colour developer coating for a pressure-sensitive copying paper.
• the nature and function of such paper is well known in the pressure-sensitive copying paper art and so will not be described further herein.
• An aqueous suspension at 47% solids content was prepared, from the following components:
• the sodium silicate, talc, China clay and reactive clay were first dispersed in the water over a period of one hour with vigorous stirring in a first mixing tank.
• the binder was then added and mixing continued for five minutes.
• the resulting slurry was then transferred to another mixing tank, and the foaming agent was then added under low shear conditions to produce a foamed aqueous suspension.
• the resultant foamed dispersion was thixotropic in character. Table III below shows the relationship between solids content, air content and viscosity. In view of the thixotropic nature of the foamed dispersion, the viscosity was measured in each case after shear thinning had occurred.
• the foamed suspension exhibited a lower viscosity than an unfoamed dispersion for an air content of the order of 12 to 13%.
• the foamed mix was coated onto 49 g/m 2 paper base in the manner described above with reference to Example I.
• the results obtained showed that the change in the character of coating mix and the addition of a foaming agent did not affect the functional properties of the coated paper thus produced.
• Empicol ESB30 is a surface active agent of the lauryl ethylene oxide sulphate type.
• any other surfactant may be used which does not inhibit the reactivity of the clay or cause the components of the suspension to flocculate.
• examples of such other surfactants are alkyl phenyl ether, alkyl phenyl ethylene oxide, alkyl ether sulphate, alkyl benzene sulphonate and alkyl sulphate.
• An aqueous dispersion of an approximately 44% solids material was prepared in two stages.
• a reactive resin slurry was first prepared from the following components using a Silverson mixer (a high shear rotating shaft mixer):
• the slurry was ground in a torrance 30S attritor for 21/2 hours and used in the following coating formulation.
• the components were added to a mixing tank with virorous stirring and, with addition of various amounts of polyvinyl alcohol as a foaming agent.
• the polyvinyl alcohol was that solid as Moviol 4/88 by Farbwerke Hoechst AG). Air was introduced into the mix as a consequence of vortex production by the mixer and of the presence of the foaming agent.
• Table IV shows the relationship between the solids content, polyvinyl alcohol content, air content and viscosity for the suspension. It will be seen that for this formulation the viscosity continually decreased as the air content increased, i.e. no "minimum” viscosity was observed.
• Example III the viscosity was measured after shear thinning had occurred.
• Coating compositions with the air contents given in Table IV were coated on to a 49 g/m 2 base paper using a laboratory blade coater.
• the coated paper was found to have an acceptable functional properties when used in a pressure-sensitive copying system as a paper which had been coated with a non-foamed composition.
• Example IV This involved further work on the formulation detailed in Example IV with a polyvinyl alcohol content of 1%. The object was to investigate the results obtained on scaling up the process.
• Example IV The components were added to a tank in the order indicated in Example IV, under vigorous stirring by rotary mixing blades. Air was then forced under high pressure through a perforated pipe located near the mixing blades at the base of the tank. Shearing was maintained during this process. Table Va shows the observed relationship between solids content, air content and viscosity. As in Examples III and IV, the viscosity was measured after shear thinning had occurred.
• the 29% air content formulation was then coated by means of a coating apparatus as shown in FIGS. 1 and 2 of the aforesaid copending application Ser. No. 590,681.
• An aqueous dispersion was prepared using the following material:
• Example VI This involved further work on the formulation set out in Example VI, with a polyvinylalcohol content of 1% but a solids content of 44%. The object was to investigate the results obtained on scaling up the process.
• Example V The components were added to a tank and sheared by means of rotary blades. Air was forced under high pressure through a perforated pipe at the base of the tank during mixing as in Example V.
• the coating mix was transferred to the mix circulation and foaming unit of the pilot plant coater described in Example V. Air was added by circulating the mix in the system. Table VIII below shows the observed relationship between solids content, air content and viscosity. It proved difficult to obtain a foam of low air content, i.e. less than 10%. Viscosity measurements were made after shear thinning had occurred.
• the 10% air content mix was then coated at a coatweight of about 10 g/m 2 , using a coating apparatus as shown in FIGS. 1 and 2 of our copending British patent application No. 29729/74.
• the properties of the coated paper were very similar when tested in a pressure-sensitive copying system to those obtained with a paper which had been coated with a non-foamed coating composition.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Paper (AREA)
• Color Printing (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (2)

Related Parent Applications (1)

Publications (1)

Family

ID=10393933

Family Applications (1)

Country Status (14)

Cited By (25)

Citations (8)

• 1974
  • 1974-08-23 GB GB3712474A patent/GB1477411A/en not_active Expired
• 1975
  • 1975-08-13 ZA ZA00755190A patent/ZA755190B/xx unknown
  • 1975-08-15 NZ NZ178399A patent/NZ178399A/xx unknown
  • 1975-08-19 CH CH1075775A patent/CH599396A5/xx not_active IP Right Cessation
  • 1975-08-20 CA CA233,827A patent/CA1026999A/en not_active Expired
  • 1975-08-20 FI FI752356A patent/FI58180C/fi not_active IP Right Cessation
  • 1975-08-20 BE BE159314A patent/BE832570A/xx not_active IP Right Cessation
  • 1975-08-21 IT IT26483/75A patent/IT1041966B/it active
  • 1975-08-21 FR FR7525910A patent/FR2282299A1/fr active Granted
  • 1975-08-21 BR BR7505374*A patent/BR7505374A/pt unknown
  • 1975-08-22 JP JP10251875A patent/JPS5731945B2/ja not_active Expired
  • 1975-08-22 NL NL7509950A patent/NL7509950A/xx active Search and Examination
  • 1975-08-23 DE DE2537704A patent/DE2537704C2/de not_active Expired
• 1977
  • 1977-04-11 US US05/786,382 patent/US4263344A/en not_active Expired - Lifetime

Patent Citations (8)

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